In that brief time around 1:30 a.m. ET Monday, friction, a parachute, and an unprecedented "sky crane" hovercraft will help take Curiosity from 13,200 miles (21,200 kilometers) an hour to zero—if everything goes to plan.

"When we proposed this plan, we were almost laughed off the project," Adam Steltzner, NASA's chief engineer for the operation, says in the new National Geographic e-book Mars Landing 2012. "People said it couldn't possibly work."

The Curiosity rover is the largest and most complex of its kind, and so, by necessity, is its landing. What's more, the process couldn't be rehearsed, because Mars's atmosphere is so different from Earth's.

Making matters worse, the rover will truly be on its own as it falls. Because of communications delays, by the time we know anything is wrong, it'll be too late to fix it.

Much is riding on the Curiosity rover, both literally and figuratively. Carrying 165 pounds (75 kilograms) of science instruments, the rover is our best shot so far at learning whether or not life ever existed, or could exist, on Mars. (Get the basics on the Curiosity, the Mars Science Laboratory rover.)

Illustration courtesy Caltech/NASA

Breakthrough

Upper and lower heat shields hard at work, Curiosity enters the Mars's upper atmosphere at 13,200 miles (21,200 kilometers) an hour (artist's conception). The impact creates so much friction that the craft's deceleration will be 90 percent complete before its parachute opens, some 80 miles (130 kilometers) lower in the atmosphere.

Having deployed its parachute and ditched its underside heat shield—exposing the Mars rover's undercarriage—Curiosity plummets a bit slower in a NASA illustration.

The 60-foot-wide (18-meter-wide) parachute is the largest and strongest ever sent to another world, according to NASA. It has to be: The falling rover will generate 65,000 pounds (30,000 kilograms) of drag force when the chute's lines snap taught.

If the parachute doesn't open on cue, the rover has no chance of landing intact—just one of many make-or-break moments within the seven minutes of terror.

"We now have a risk analysis that says [the landing] has a 99 percent likelihood of succeeding," NASA's Steltzner says in Mars Landing 2012. "That assumes all the parts will operate and deploy as they should.

"Given the circumstances and essential timing of all the maneuvers, we're definitely asking a lot. That's what's keeping me up at night."

Illustration courtesy Caltech/NASA

Hovercraft

Having ejected the lower heat shield and the parachute, the sky crane—with the rover in its belly—fires retro-rockets to hover 66 feet (20 meters) above the surface of Mars. Soon the hovercraft will loosen its grip on tethers holding Curiosity, allowing gravity to pull the rover to the ground.

The sky-crane maneuver, completely new with this mission, was necessary to accommodate the sheer weight of Curiosity. The "air bag"-dependent, bounce-and-roll landing maneuver used with earlier, and much smaller, Mars rovers couldn't have protected the nearly 2,000-pound (907-kilogram) Curiosity.

"We know the sky-crane maneuver looks crazy," Steltzner says in Mars Landing 2012. "It even looks crazy to us. But it's the result of careful, reasoned engineering thought, and we have been beating on it for almost a decade."

Curiosity lands on its feet in a NASA illustration. The rover should be far more efficient at data-capturing than any of its predecessors, partly because Curiosity is much better equipped to land near its study targets inside Gale Crater.

As the sky crane rockets toward a crash landing safely afield of Curiosity, the rover stretches its legs.

Armed with cameras, a rock-vaporizing laser, weather sensors, spectrometers, and tools for identifying minerals and organic compounds, Curiosity is to spend at least the next two years searching mainly for signs of past life on Mars.